1. Field of the Invention
The present invention relates to a servo signal recording apparatus that records a servo signal for head tracking servo in a magnetic tape data storage system for a computer, and more specifically relates to a servo writer for data storage tape with superior head tracking servo characteristics.
2. Description of Related Art
Magnetic tape has a variety of applications such as audio tape, video tape and computer tape. Although particularly in the field of data backup tapes, magnetic tapes with a recording capacity of 800 GB or more per reel have been commercialized following increases in the capacity of hard disks for backup. High capacity backup tapes have been proposed with the development hereafter of techniques for backing up data exceeding 4 TB.
One conceivable method of increasing the capacity of magnetic tape is, for example, to make the magnetic tape thinner to increase the tape length per reel, without increasing the reel diameter of the magnetic tape per reel. Another method involves shortening the recording wavelength of data recorded on the magnetic tape to increase the longitudinal recording density of the magnetic tape. A further method involves reducing the recording track width of the magnetic tape to increase the lateral recording density of the magnetic tape (high density recording technique).
When the recording track width is reduced by employing a high density recording technique for magnetic tape, the magnetic head is unable to accurately follow the recording track due to the lateral motion of the magnetic tape during tape reproduction or the like, making errors more likely. In view of this, currently, systems that are able to record a servo signal to a magnetic layer or a back-coat layer of the magnetic tape during manufacture, and reproduce the servo signal from the magnetic tape to perform tracking servo in a tape drive have become mainstream.
As for servo systems, there is a magnetic servo system and an optical servo system. With the magnetic servo system, a servo signal is magnetically recorded to a magnetic layer of the magnetic tape, and the servo signal is magnetically read in the tape drive to perform tracking servo. With the optical servo system, a servo pattern constituted by a recessed array is formed on a back-coat layer on the magnetic tape with laser irradiation or the like, and the recessed array is optically read in the tape drive to perform tracking servo.
These servo systems enable the magnetic head to follow each track when recording data to magnetic tape or reproducing data from magnetic tape, even when the magnetic tape moves laterally relative to the magnetic head. Specifically, the servo signal recorded on the magnetic tape is firstly read with a servo head. Next, the read servo signal is analyzed and the lateral position of the magnetic tape in a head unit that includes at least a data recording head and a data reproducing head is controlled to allow the data recording head or the data reproducing head to follow each track. This enables information to be recorded to the correct position on a magnetic tape, and information recorded on a magnetic tape to be correctly reproduced.
Disclosed in patent document 1 (JP H8-30942 A) is a timing based servo system constituting an exemplary servo system. With this timing based servo system, the servo signal is recorded to magnetic tape in a pattern where the servo signal is at an angle to the lateral direction of the magnetic tape. The head position is confirmed from the time intervals between the peaks of the reproduction waveform when the servo signal is reproduced.
Disclosed in patent document 2 (specification of U.S. Pat. No. 6,226,688) is a head tracking servo method capable of recording and reproducing data without error by allowing the reproducing head to correctly follow a recording track at high speed, even in the case where the recording track width is further reduced and tape speed increased, thereby enabling compatibility with the increased recording density of magnetic tape.
However, a problem with the servo signal written to magnetic tape by the servo write head disclosed in patent documents 1 and 2 is that tracking servo cannot be performed at high speed and with high precision in a tape drive.